Interpretive Summary: This report is the first recorded outbreak of cryptosporidiosis in a group of cats. Cats were housed in a clean research facility, received fresh food and water daily, and litter pans were cleaned daily. Over a 22 day period all 18 cats housed in the same room but in separate cages excreted oocysts of Cryptosporidium felis, a parasite infectious for humans. During the course of infection 8 cats also excreted Giardia duodenalis Assemblage F, a parasite known only to infect cats. All cats appeared to have good appetites and none had diarrhea or other signs of illness. Because C. felis is zoonotic these findings suggest that care should be taken by veterinary health care providers and others in close contact with cats, even when cats appear healthy and asymptomatic.

Technical Abstract:
Eighteen cats, 3 to 6 mo of age, bred and housed in a closed colony, were transferred from that colony and placed in separate stainless steel cages in a building designed for housing animals. At daily intervals, feces were collected from the litter pans in each cage, cages were cleaned, and fresh food and water were provided. Beginning 4 weeks after the transfer, oocysts of Cryptosporidium felis, a zoonotic parasite primarily infecting cats, were detected in the feces of two cats. For the following 21 days, with minor exceptions, feces from each cat were collected daily and examined by immunofluorescence microscopy. Feces from every cat were also examined by molecular methods that included DNA extraction, 18S rDNA gene amplification, and DNA sequence analysis. Within those 22 days every cat became infected with Cryptosporidium felis and excreted oocysts for 6 to 18 days. Although Cryptosporidium spp. has been reported in cats worldwide, this is the first report of a spontaneous outbreak among a large number of cats. Eight of these 18 cats also excreted cysts of Giardia duodenalis assemblage F, a genotype reported only in cats. Six Giardia infections were concurrent during part of the patency with C. felis infections. All cats appeared healthy and asymptomatic. Neither diarrhea nor other signs of illness were observed in any of the cats during this time. Because C. felis is zoonotic these findings suggest that care should be taken by veterinary health care providers and others in close contact with cats, even when cats appear healthy and asymptomatic.